Some of the most powerful explosions in the Universe are gamma ray bursts, capable of blasting a beam of death halfway across the galaxy. In just the last few years, astronomers have discovered a tremendous amount about these blasts, and what’s actually causing them. The answer, of course, is that it’s more complicated than we thought.
Artemis I (NASA)
Europa Clipper (NASA Jet Propulsion Laboratory)
Gamma-ray Bursts (NASA)
PODCAST: Ep. 36: Gamma-Ray Bursts (Astronomy Cast)
Vela (satellite) (Wikipedia)
Gamma ray bursts – types (Swinburne)
Viewing Short Gamma-Ray Bursts From a Different Angle (Frontiers in Astronomy and Space Sciences)
Gamma ray burst afterglow (Swinburne)
Gamma Ray Bursts (Chandra X-ray Observatory)
IMAGE: First visible light from GRB 050709 (ESO)
Neutron Stars (CalTech)
Neutron Star Binaries (University of Frankfurt)
There’s gold in them there Gamma Ray Bursts (University of Warwick)
Mars Odyssey (NASA)
Wind Spacecraft (NASA)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast Episode 592. Gamma-ray bursts updated. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, Senior Scientist for the Planetary Science Institute, and the director of CosmoQuest. Hey Pamela, how you doing?
Dr. Pamela Gay: I’m doing well. Our country has moved on into a time where science is constantly being discussed –
Dr. Pamela Gay: – and there is a Moon rock! A Moon rock in the oval office right now!
Fraser: I’ve seen the pictures. That’s so cool, yeah! Yeah, it’s a cool – it looks big in the…
Dr. Pamela Gay: Well, and Moon rocks come in many different sizes. And if you’re gonna show one off, don’t show off the dust grains.
Fraser: Yeah, show off one of the big ones.
Dr. Pamela Gay: Yeah!
Fraser: Yeah, they brought back something like 200 kilograms of rock from the moon. From dust, and even that dust is of high value.
Dr. Pamela Gay: Oh yeah.
Fraser: But there are a couple of fairly large rocks. And to have a cool Moon rock, that’s – you can imagine anyone who comes in and wants to talk about the future of the moon exploration has to stare at that Moon rock and go, “Yeah, you wanna get more of that?” 2024, let’s go!
Dr. Pamela Gay: Yup. It’s not going to be 2024 unless it’s –
Fraser: 2024! There’s no reason why – actually, good news. I don’t know if you were watching the SLS hot fire test and the abort that went a minute into it, but it looks like there was no big problem. That they had very tight constraints on it, their test set up ran a little out of its parameters, and they shut it down. So, there’s nothing very dangerous, and they’re gonna be able to restart the test within a couple of weeks probably.
Dr. Pamela Gay: Well, and so they’ve decided they’re gonna do another green test?
Frasier: They haven’t said. They have to. But the point just being they’re not gonna be spending months or even years taking everything apart, figuring out why there was –
Dr. Pamela Gay: Right.
Fraser: – problems. The problem was a sensor to study the test, from what I understand, failed. And so, the issue is minor, the fix is easy, and the test can be done again in a very rapid period of time. So, hopefully, we won’t see a gigantic delay on the schedule. The gigantic delay on the schedule will come from everything else adding up.
Dr. Pamela Gay: And one of the issues that they’re dealing with is the hardware that they’re testing is the exact same hardware that they’re planning to use for Artemis I Mission I.
Frasier: Europa Clipper.
Dr. Pamela Gay: And so, they’re being extremely conservative, ‘cause they don’t have another core stage waiting to go, –
Dr. Pamela Gay: – and they can only refill these nine times. They’re not reusable. And each time they fill them to run the test, that super cold liquid, it does damage.
Fraser: Yeah. So, once its tests are complete, it will be moved and launched. This is the one that will launch. The first one. And then it’s gonna lose its beautiful RS-25 engines into the ocean, which makes me sad.
Dr. Pamela Gay: But it may go around the moon.
Fraser: Yeah, I know. It’s totally cool. All right, so some of the most powerful explosions in the universe are gamma-ray bursts, capable of blasting a beam of death halfway across the galaxy. In just the last few years, astronomers have discovered a tremendous amount about these blasts, and what’s actually causing them. The answer of course is that it’s more complicated than we originally thought. And we’ll talk about it in a second, but first, here’s our break. All right, this episode of Astronomy Cast is brought to you by test sensors. Reliable test sensors.
And we’re back. All right Pamela, it’s funny. So, in setting up this week’s episode, I looked back through the schedule – whenever I brainstorm ideas for episodes – and I’m sure you do the same as well – you look back at what interesting stories have broken and go, “Have we covered this?” And gamma-ray bursts is all in the news in the last couple of weeks and years. And I’m like, “Of course we’ve covered gamma-ray bursts, but when?” And it turns out, 500+ episodes ago was the last time we seriously talked about gamma-ray bursts. So, it’s an entirely new field. And so, it’s time for a refresh.
Dr. Pamela Gay: And what gets me is while our little podcast has been around for 15 years, we’ve been only going out on NowMedia Houston 21 for a week. Two weeks.
Fraser: Oh. Right, so you’re saying Houston has never heard of gamma-ray bursts then?
Dr. Pamela Gay: Exactly.
Dr. Pamela Gay: We’re going to explain them for the very first time.
Frasier: But I think that even the language that we use, the context that we give is gonna be different than what we would have done – I can’t bring myself to listen to our old episode – but it’s a different world now. So, what is a gamma-ray burst?
Dr. Pamela Gay: So, as the name implies, when there is a burst of extremely high-energy light with wavelengths so short that the light is in the gamma-ray part of the spectrum, that light hitting our detectors is called a gamma-ray burst. We’re lazy when we name things sometimes. Gamma-ray bursts were first detected back in the 1960s by the Vela missions that were launched to look for space tests of nuclear weapons by the soviets.
But instead of seeing any against-treaty nuclear tests, this spacecraft, the suite of spacecraft actually, were able to catch all these different little gamma-ray bursts. And using the timing of when each of the different spacecraft detected the gamma-rays, they were able to figure out, “Okay, so this difference in timing means the light started over there, hit this one first, then this one, then this one.”
And over the years, they figured out they were coming from all over the sky. So, up through the 1990s, we didn’t know if these were coming from other galaxies, we didn’t know is this something related to the old stars in the sphere of material around our galaxy. And then in the 1990s, we finally were able to start zeroing in on the sources of at least some gamma-ray bursts.
Fraser: And I think this is where in the beginning, there was just, “Oh yeah, there are these explosions of gamma radiation coming from some random spot in the sky.” We were able to avoid world war three, which was convenient. Astronomy should never begin a World War III. But then, as astronomers started to examine these things, they started to realize that they’re not all created equally.
Dr. Pamela Gay: So, the first thing that we zeroed in on was gamma-ray bursts seemed to come in two different lengths. There were the long ones that were more than two seconds, and there were the short ones that were less than two seconds. And by more and less, the longer ones could last for days in the longest cases, and the shortest ones could last for fractions of a second.
Dr. Pamela Gay: Hundred and forty milliseconds. So, looking at this distribution where there’s a stack of them that are short, a broader stack of them that were long, we started to get hints that there’s different physics behind them. And the first time we caught what we now call the “Optical Afterglow” of one of these gamma-ray bursts, we’d been able to steer a spacecraft that caught the gamma-rays to then look at that area in x-rays and see is there this other component of light that’s easier to focus on? That maybe will tell us where to focus an optical telescope. The problem that we have is a gamma-ray telescope is basically the sky had a burst somewhere.
Fraser: Right. It’s like watching meteor showers with people, and you’re like, “Oh, there’s a good one.” And then they go, “Where?” And you’re like, “It’s gone.”
Dr. Pamela Gay: Yeah.
Fraser: “You missed it.” And then, “Oh, one over there!” “Oh, you missed it.” And so, even if you’re hanging out with a bunch of your friends and you’re all trying to scan like, “Did you see that one?” “Yeah, I saw it.”
Dr. Pamela Gay: No.
Fraser: But someone else didn’t see it, ‘cause it’s too quick. ‘Cause they’re happening so fast.
Dr. Pamela Gay: But finally, they were able to zero in on it in the x-rays, and then many hours later, catch the last faint bits of optical light associated with what they decided to call a “Hypernova.” Some sort of a nova in a very distant galaxy. And from that first discovery in the ‘90s, we have begun to over and over and over see these optical afterglows from long gamma-ray bursts. And for a couple of decades, we consistently explained, “Well, these are hypernova, they’re caused by some sort of a gigantic star in its final days. And for reasons that we don’t know, maybe its orientation, it has a massive magnetic field, and it is directing gamma-rays at us that we are seeing.”
And the confusing thing was we see supernovae all the time. And most of them don’t have gamma-ray bursts associated with them. So, the question starts to be, “What weirdo special physics allows these amazing pulses of high-energy light to come traveling our direction?”
Fraser: Well, we’ll talk about weirdo special physics in a second, but first we’ve got a commercial break. And we’re back. So, I guess people are familiar with the term “Supernova,” and I think people are probably familiar with that term “Hypernova.” And so, hypernova is a gamma-ray burst. You can just now throw away the idea of a hypernova and just replace it with a gamma-ray burst. And now, –
Dr. Pamela Gay: Exactly.
Fraser: – as you’re gonna learn today, a gamma-ray burst is a bunch of different things. But when you see a gamma-ray burst, what is the weird thing, the weird physics that you’re observing when you observe a gamma-ray burst?
Dr. Pamela Gay: Well, what we now know is that for long, and only for long gamma-ray bursts, –
Fraser: Only long bursts, yeah.
Dr. Pamela Gay: – you have two previously massive stars that are in orbit around each other. One of these started out a bit bigger, it has gone through life, it has gone supernova, it has crunched down into a neutron star, and it’s hanging out next to its slightly smaller, but not that much smaller, companion. And when that still massive, but not as massive, companion goes supernova in its own right, trying to form its own neutron star, it explosively sheds its outer atmosphere. And this outer atmosphere goes, and it hits that OG neutron star.
And it gets consumed in the process. And neutron stars have massive magnetic fields – and this is gonna come up later again today – and the interactions of this original neutron star in the system, it’s magnetic field, everything else that’s going on can drive it to spin faster, can drive it to in some cases go supernova again, but in its own special way where it’s not really a supernova. But it’s getting so much mass piled onto it that it collapses down into a black hole. And all the physics of that older original neutron star, that’s the source of the gamma-ray bursts.
Dr. Pamela Gay: It’s the other star that’s the source of the light of the supernova that we see in the optical afterglow.
Fraser: And so, we know that when a massive star with many times the mass of our own Sun goes off as a supernova, it’s remnant that it leaves behind, if it’s not super big, then it’s left with this neutron star. And it starts out spinning very rapidly, and we call that a pulsar. And then it slows down and slows down, and eventually is less pulsar-y.
But, it’s this binary interaction with two massive stars. One goes off, you get a neutron star, a pulsar, and then the other one goes off shortly afterwards, bombards it with material, and then spins it up, cranks its magnetic field, and makes a magnetic monster. And so, you say the supernova’s coming from the star that goes off, but the gamma-rays are coming from the magnetar?
Dr. Pamela Gay: Well, we don’t even know if it started as a magnetar. It was just a neutron star.
Dr. Pamela Gay: But the insanity of this is material can’t just go straight from that first start to the second star. It has this annoying property called, “Angular Momentum.” So, the material that’s coming ends up spiraling around that neutron star forming a little tiny accretion disk, as that material drives down towards the neutron star. And that spinning neutron disk, that is a source of jets and gamma-rays. And if too much of that material makes it onto that companion neutron star, it’s gonna collapse down into a black hole.
Dr. Pamela Gay: It’s a two-system dynamic. And it’s the transfer of that material into this new accretion disk creating these new jets. This is that gamma-ray burst that we’ve been seeing.
Fraser: Interesting. And which one does this explain? The short or the long?
Dr. Pamela Gay: This explains the long and only the long.
Dr. Pamela Gay: And if you wanna read more about these, first of all, don’t trust astronomers to name things.
Dr. Pamela Gay: But the best-studied so far is GRB 190114. This means it was a gamma-ray burst that went off on January 14th, 2019.
Fraser: So, we know that there are magnetars – I think I mentioned this earlier, maybe not on this show – but there’s only a handful. There’s only 30 magnetars ever found. And so, clearly something very special is going on. So, do we think that the magnetars were formed as a result of the gamma-ray burst, or were they already there, and that’s what causes the burst, because you’ve got a magnetar there? They’re somehow involved.
Dr. Pamela Gay: It’s unclear right now. And –
Dr. Pamela Gay: – magnetars are one of these weird things that we finally have sufficient technology in our telescopes to be able to study them in ways never before. So, a magnetar, to back up, is a special kind of neutron star. It can be a pulsar; it doesn’t have to be a pulsar. What it has to have is a massive magnetic field. And when those magnetic field lines break and rearrange, just like we see happening with solar flares in our Sun, instead of creating a burst of particles capable of creating the aurora we see here on Earth, magnetars when their field lines break and recombine can give off massive amounts of gamma-rays. How exactly you spin something up and create this magnetic field?
Dr. Pamela Gay: We don’t know if there’s only one way. But it appears that this kind of a gamma-ray burst might be one of the ways you do it.
Frasier: Huh. That the supernova, the nearby supernova, forms a monster.
Dr. Pamela Gay: Yeah.
Frasier: It’s like its supervillain origin story.
Dr. Pamela Gay: And what’s kind of amazing is that supervillain that has just been born creates gamma-rays that maybe will create Spider-Man later.
Frasier: I believe it’s the Fantastic Four.
Dr. Pamela Gay: But beyond that, may create a source of short-period gamma-ray bursts.
Frasier: Right. All right, so then we will talk about the other kinds of gamma-ray bursts, and how they may or may not be connected. But first, it’s time for another break. And we’re back. All right, so we’ve talked about – and you were very clear about this – long gamma-ray bursts. But as we mentioned, those are not the only kinds of gamma-ray bursts. The tricker ones to see are those ones that are like those meteors that disappear within moments. The short-period gamma-ray bursts. So, talk about those, and then what we think is causing them.
Dr. Pamela Gay: So, there appears to be two kinds of short-period gamma-ray bursts. The easy to understand one, if easy is a word that can even be used in this conversation, is the kind that occurs when two neutron stars – so, maybe the future of one of these systems we just discussed – when these two neutron stars are orbiting next to each other. Over time, they can get closer and closer and closer until they merge into a single object, give off a pulse of gamma-ray bursts, particles, gravitational waves. And we can detect all of that here on Earth. This was seen back in 2017 for the first time –
Fraser: Yeah, the Kilonova.
Dr. Pamela Gay: It’s amazing. And this is one of the major contributors to gold. If you’re wearing jewelry, it may have come from a short gamma-ray burst that had a smooth pulse of light associated with the merger of two neutron stars. That may or may not have been magnetars.
Fraser: Right. So, and I was gonna say this, that it’s a different situation. But you’ve got a neutron star and a supernova going off potentially turning into a neutron star in one situation, causing –
Dr. Pamela Gay: Long.
Fraser: – a gamma-ray burst, the long gamma-ray burst, or you’ve got two neutron stars colliding with each other causing the short gamma-ray burst.
Dr. Pamela Gay: And we still have a third scenario.
Fraser: Right. We’ll talk about that in a second, but I guess what I’m saying is that a binary star system could give you one kind of gamma-ray burst, and then give you the other kind of gamma-ray burst some period of time later.
Dr. Pamela Gay: And in-between, it might even have that third kind of gamma-ray burst.
Fraser: Okay, what is the third type of gamma-ray burst?
Dr. Pamela Gay: So, there are magnetars out there that when their magnetic field lines rearrange, give off magnificent bursts of gamma-rays that are flicker-y, flare-y. And they come in a whole variety of powers, for lack of a better word. Back on December 27th, 2004, one went off in our own galaxy on the other side of the center of the galaxy. And it was so bright that the light went through the sides of space telescopes and saturated –
Dr. Pamela Gay: – the detectors.
Fraser: Just wrap your head around that idea. Imagine you have your telescope, you point it at, I don’t know, Jupiter, and the sun gives off a flare that’s so powerful, it vaporizes the side of your telescope and makes it very bright. That’s what happened. The telescopes were fine, but they detected it.
Dr. Pamela Gay: Yeah, but the fact that it was so bright, it was hard to study because everything was fairly saturated. And while it looked kinda like a short-period gamma-ray burst, it wasn’t bright enough to be classified as a gamma-ray burst. And so, people started asking the question, “Can short-period gamma-ray bursts that don’t have that smooth profile, can the flicker-y flare-y ones, can those maybe be related to magnetars?” And we finally got the answer. And here, I’m just gonna take a moment to quote a press release of work done by the researcher Kevin Hurley, on a gamma-ray burst that was detected on April 15th, 2020. This is how it was detected. And this is, I think, one of my favorite stories in astronomy:
“Shortly before 4:42 a.m. Eastern Daylight Time on that Wednesday, a brief powerful burst of x-rays and gamma-rays swept past mars, triggering the Russian high-energy neutron detector aboard NASA’s Mars Odyssey Spacecraft. Mars Odyssey, – “
Dr. Pamela Gay: “– which has been orbiting the planet since 2001. About 6.6 minutes later, the burst triggered the Russian Konus instrument aboard NASA’s wind satellite, which orbits a point between Earth and the sun, located about 930,000 miles (1.5 million kilometers) away. After another 4.5 seconds, the radiation passed Earth, triggering instruments on NASA’s Fermi gamma-ray space telescope, and the European Space Agency’s integral satellite. The burst lasted only 140 milliseconds.”
Fraser: Wow! And that was one of these magnetar blasts.
Dr. Pamela Gay: And what was amazing is because the burst was so short, and detected by so many different things, they’re able to zero in on where it had to be in the sky to have these precise timings as each different instrument was struck with the gamma-rays. And when they turned to look with telescopes, they were able to find that it was in a plain jane galaxy, NGC 253, in the direction of the Sculptor constellation. It was a magnetar. It had the same flickering pattern that was seen back in 2004, but the light wasn’t saturated. And so, that distant object gave off light in the exact same way –
Fraser: Mm-hmm. But they could observe it.
Dr. Pamela Gay: They could observe it.
Dr. Pamela Gay: And it was so much brighter, –
Dr. Pamela Gay: – that it indicated we got lucky in 2004. And magnetars are totally capable of giving off massive, short-period gamma-ray bursts. So, to go back to our example, gamma-ray bursts in 190114C, where we had a star exploding, speeding up the neutron star next to it, triggering the Gamma-ray burst, collapsing down and forming a neutron star, that produced a long gamma-ray burst. Over time, if that companion star became a magnetar as may be possible, it could flicker and flare and give off one kind of short gamma-ray burst. And in the fullness of time, when these two finally merge together, that will give off the other short-period kind of gamma-ray burst.
Fraser: Wow, so everything comes back to magnetars.
Dr. Pamela Gay: Everything.
Fraser: That’s amazing. And I think it’s important to understand just how powerful these gamma-ray bursts – how much energy is actually being given off. I mentioned that it fires out a death beam half across the Milky Way. How close can you be to a gamma-ray burst, and it’s starting to cause you a problem?
Dr. Pamela Gay: If you had one within a few thousand light-years of Earth pointed at us, it could ionize the side of our atmosphere it struck, which would be bad for everyone on the planet.
Fraser: Mm-hmm. So, a Gamma-ray burst going off within, say, a few thousand light years, which is an enormous distance in space, is a –
Dr. Pamela Gay: Pointed at us.
Fraser: – is an extinction-level event for a good portion of life on Earth. And –
Dr. Pamela Gay: Yeah.
Fraser: – even one that is halfway across the Milky Way will wreck our ozone layer and cause significant damage. It’s a mind-bending quantity of energy.
Dr. Pamela Gay: And there are some hints that we might’ve had one of these extinction-level events in the past. But that’s for a different show.
Fraser: Yeah. Well yeah, your favorite topic. Extinction-level events. Thanks, Pamela! That was amazing! I love the update. I’ve mentioned this. So, for so many of the mysteries that we look at, dark matter, dark energy, I’m still having arguments with people about whether dark matter is even a thing. And I believe yes, they believe no, but the point being we may know that it’s a thing, but we don’t know what thing it is. What’s causing it. And yet, here’s something like gamma-ray bursts that we have watched from over the course of 50 years to go from, “Here’s something interesting,” to, “Oh, it’s a lot more complicated than we thought, and here’s the explanation.” That’s beautiful! That’s science! I love it!
Dr. Pamela Gay: And it’s awesome.
Fraser: Yeah, totally. All right, thank you Pamela. Do you have some names for us this week?
Dr. Pamela Gay: I do. So, as always, we are supported entirely through donations. And if you want to become one of the people that allows us to do this show and pay our editors a fair wage and to make sure that we have transcripts and show notes and all this added material, go to patreon.com/astronomycast and join our community.
This week, I would like to thank Martin Dawson, Kenneth Ryan, Steven Coffey, Cemanski, Glenn McDavid, Benjamin Davies, Brento, Nalia, The Air Major, Shannon Humber, Ryan James, Kseniya Panfilenko, Sean Freeman (Blixa the cat), Nial Bruce, Gabriel Gauffin, Neuterdude, Jordan Turner, Rayvening, Allen M Price, Mark Van Kooy, Daniel Loosli, and Kimberly Rieck. Thank you all so much for allowing us to do what we do.
Fraser: Thank you everybody, thank you Pamela, and we’ll see you all next week.
Dr. Pamela Gay: Buh-bye, everyone.
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